Shining Light on Photosynthesis in the Harmful Dinoflagellate Karenia mikimotoi–Responses to Short-Term Changes in Temperature, Nitrogen Form, and Availability

Karenia mikimotoi is a toxic bloom-forming dinoflagellate that sometimes co-blooms with Karenia brevis in the Gulf of Mexico, especially on the West Florida Shelf where strong vertical temperature gradients and rapid changes in nitrogen (N) can be found. Here, the short-term interactions of temperature, N form, and availability on photosynthesis–irradiance responses were examined using rapid light curves and PAM fluorometry in order to understand their interactions, and how they may affect photosynthetic yields. Cultures of K. mikimotoi were enriched with either nitrate (NO3−), ammonium (NH4+), or urea with varying amounts (1, 5, 10, 20, 50 µM-N) and then incubated at temperatures of 15, 20, 25, 30 °C for 1 h. At 15–25 °C, fluorescence parameters (Fv/Fm, rETR) when averaged for all N treatments were comparable. Within a given light intensity, increasing all forms of N concentrations generally led to higher photosynthetic yields. Cells appeared to dynamically balance the “push” due to photon flux pressure and reductant generation, with consumption in overall metabolism (“pull” due to demand). However, at 30 °C, all fluorescence parameters declined precipitously, but differential responses were observed depending on N form. Cells enriched with urea at 30 °C showed a smaller decline in fluorescence parameters than cells treated with NO3− or NH4+, implying that urea might induce a photoprotective mechanism by increasing metabolic “pull”.

Submesoscale Instability in the Straits of Florida

The Florida Current (FC) flows in the Straits of Florida (SoF) and connects the Loop Current in the Gulf of Mexico to the Gulf Stream (GS) in the Western Atlantic Ocean. Its journey through the SoF is at time characterized by the formation and presence of mesoscale but mostly submesoscale frontal eddies on the cyclonic side of the current. The formation of those frontal eddies was investigated in a very high resolution two-way nested simulation using the Regional Oceanic Modeling System (ROMS). Frontal eddies were either locally formed or originated from outside the SoF. The northern front of the incoming eddies was susceptible to superinertial shear instability over the shelf slope when the eddies were pushed up against the slope by the FC. Otherwise, incoming eddies could be advected relatively unaffected by the current, when in the southern part of the straits. In absence of incoming eddies, submesoscale eddies were locally formed by the roll-up of superinertial barotropically unstable vorticity filaments when the FC was pushed up against the shelf slope. The vorticity filaments were intensified by the friction-induced bottom layer vorticity flux as previously demonstrated by Gula et al. (2015b) in the GS. When the FC retreated further south, negative vorticity West Florida Shelf waters overflowed into the SOF and led to the formation of submesocale eddies by baroclinic instability. The instability regimes, hence, the submesoscale frontal eddies formation appear to be controlled by the lateral ‘sloshing’ of the FC in the SoF.

Estimating the Thermodynamic and Dynamic Contributions to Hydroclimatic Change over Peninsular Florida

In this study we examine the thermodynamically and dynamically forced hydroclimatic changes in the four representative seasons over Peninsular Florida (PF) from an unprecedented pair of high resolution regional coupled ocean-atmosphere model simulations conducted at 10km grid spacing for both the atmospheric and the oceanic components forced by one of the global climate models that participated in CMIP5. The model simulation verifies reasonably well with the observations and captures the distinct seasonal cycle of the region. The projected change in the freshwater flux in the mid-21st century (2041-2060) relative to the late 20th century (1986-2005) shows a precipitation deficit in the summer over PF, which is statistically significant. This projected change in freshwater flux over PF is enabled by the strengthening of the anticyclonic North Atlantic Subtropical High Circulation with corresponding changes in divergence of moisture, advection of moisture from changes in the winds and in the change in humidity gradient, and from the change in moisture flux convergence by the transient eddies. These changes suggest that a future warm climate could witness a drier summer over PF at the expense of a wetter West Florida Shelf. The analysis conducted in this study reveals that the changes in atmospheric circulation have a significant impact on the hydroclimate, far more than that implied by the Clausius Clapeyron Equation from changes in temperature.

Seasonal abundance and diel behavior of roughneck shrimps (species of Rimapenaeus Pérez Farfante & Kensley, 1997) (Decapoda: Dendrobranchiata: Penaeidae) in northwestern Florida Bay, Florida, USA

A large number of roughneck shrimps, Rimapenaeus Pérez Farfante & Kensley, 1997, were collected in northwestern Florida Bay, southern Florida over four consecutive years (2000–2003) of monthly sampling during new-moon periods. Juveniles of Rimapenaeus spp. were more abundant than pink shrimp Farfantepenaeus duorarum (Burkenroad, 1939) juveniles, which are well-recognized and abundant inhabitants of Florida Bay. High Rimapenaeus spp. abundance was unexpected because the genus was previously reported only as occasional in Florida Bay. The populations of Rimapenaeus spp. were composed of late postlarvae and immature juveniles, suggesting that the northwestern border of Florida Bay serves as a nursery ground for this species. A clear seasonal recruitment pattern was observed with large peaks of postlarvae and small juveniles occurring in summer-fall and large juveniles in spring. The summer-fall peaks occurred during months with high mean water level and sea surface temperature; these two factors significantly predicted Rimapenaeus spp. abundance. Overnight hourly behavioral studies revealed that Rimapenaeus spp. juveniles were almost exclusively present in the water column during the dark hours of the ebb tide during current speed minimum. Juvenile abundance significantly differed between moon phases with shrimps being virtually absent during the illuminated full moon. These results indicate that Rimapenaeus spp. are phototactic negative, which may explain the low presence of this species in previous Florida Bay surveys conducted during daylight hours. This study highlights the previously unrecognized contribution of the abundance of juveniles of Rimapenaeus spp. to benthic-oriented crustacean communities of western Florida Bay and its border at the southwestern Florida Shelf.